While connected to yuor computer:
1) Hold the Home and sleep button until theiPod turns off.
2) Keep holding until the iPod turns back on with the Apple Logo.
3) Once the Apple logo appears, let go of the sleep button, but keep holding the home button.
4) After some 20 seconds or so, the Apple logo will turn to the iTunes + Cable image. You can lot go oh thehome button now, and iTunes will now restore.

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b) How much FREE space is available on your main harddisk? C:\ for Windows, and Macintosh HD for Mac OS X